Power transformers are widely used for voltage conversion and include primary and secondary windings which are physically separated from each other. The windings are coupled electromagnetically through a ferromagnetic core. Various construction techniques have been adopted to meet the mechanical and electrical requirements of various transformer designs. For example, the use of a unitary bobbin having three flanges which permits the winding of both primary and second coils on the same bobbin is known. The aperture of the bobbin fits over the middle leg of an E-core transformer winding. The use of injection molding encapsulation for paper-wound flyback transformers and the like is taught by U.S. Pat. No. 3,626,051. The encapsulation of current transformers is known from U.S. Pat. No. 4,199,743. These patents address the numerous problems which must be overcome to encapsulate a transformer assembly, however, encapsulation of power type transformers has not been performed.
It is known that power transformers are not perfectly efficient and that resistive losses in the windings result in the generation of heat in the transformer assembly. Other sources of heat include core losses which result in heating of the core material. It has been conventional to expose as much of the windings as practical to the air as an aid in the dissipation of this heat. Totally insulated power supplies which are employed in DC and AC power supplies are generally produced as an assembly including a plastic housing, transformer, internal wiring, strain relief for the secondary and primary cords (if used), and electronic devices and/or thermal protective devices.
The transformers used in the above applications generally are produced by prior well known technologies. This includes tape insulated primary and secondary windings which interfere with the elimination of heat produced in the windings. This condition is aggravated by then enclosing the transformer within a plastic or metal housing which greatly increases the difficulty in the elimination of heat by nature of trapping a large air volume around the transformer, and by the thermal insulation value of the housing itself. Major disadvantages of prior known transformers include this poor thermal performance, the high volume required of the total assembly compared to that of the transformer itself, the high cost of the materials for the power supply, the high labor costs for the assembly of all the components, and the high risk of quality defects associated with the large number of components and operations required for their assembly. In the case of wall plug-in power supplies, the thermal and volume disadvantages combine to severely limit the power which can be produced in these designs.
Therefore, there is a need for an encapsulated transformer or power supply which can be employed in a safe and economical manner which overcomes the above problems.